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Evolution Explains Why Our Fingers Become Pruney in Water

Have you ever wondered why your fingers become wrinkled and pruney after you soak in a bath? Commonly, the explanation was simply that the wrinkles were a result of your skin absorbing water. That much is somewhat true; the water causes the blood vessels to constrict, drawing the skin inward. Though the volume is decreased, the amount of skin is the same, so the skin wrinkles, New Scientist explains. However, that study does not explain why the process does not occur, as scientists have known since the 1930s, in patients with nerve damage, nor does it fully explain why the rest of our skin does not become pruney to the same degree. In fact, a study published in the journal Biology Letters and conducted by researchers at Newcastle University in the United Kingdom reveals a new theory: our hands evolved to wrinkle in order to grip wet objects.

This idea was first presented in a 2011 paper published in the journal Brain, Behavior and Evolution. The Newcastle researchers decided to put this idea to the test. They asked 20 volunteers to soak their fingers in warm water over the course of 30 minutes. Then researchers measured how much time it took volunteers to move wet glass marbles and fishing weights from one container to another. The time was compared with the time taken for the volunteers to move the same objects with dry fingers.

The researchers found that, on average, pruney hands do help us grip wet items better. Volunteers were able to move the wet objects 12 percent more quickly than with dry hands. With dry objects, wrinkled hands were able to move them at about the same speed.

Study coauthor Dr. Tom Smulders said in a statement that the theory certainly held water. "Going back in time this wrinkling of our fingers in wet conditions could have helped with gathering food from wet vegetation or streams," he stated. "And as we see the effect in our toes too, this may have been an advantage as it may have meant our ancestors were able to get a better footing in the rain."

One issue arises. If we are equally adept at holding wet and dry items, why aren't our hands wrinkled all the time? The scientists admit that they do not know, but they suggest that pruney hands may limit our hands' sensitivity or make them more susceptible to pointed objects.

Researchers plan to see if similar wrinkling appears in other primates, as it has only been verified in macaques and, obviously, humans.